1. Field of the Invention:
The present invention relates generally to filtering systems, and more particularly to a filtering system for effectively filtering the water of aquariums for tropical or salt-water fish, the water of fish-farming ponds, and/or any other type of fish-farming water.
2. Description of the Prior Art:
Conventional filtering systems are fish-farming water include, for example, in the case of a water tank, the so-called internal filtering type in which an intake frame is installed upon the bottom of the tank, with glass wool, sand, or the like, spread thereover, and a lift pipe extending to the water surface is mounted upon the frame, the treated water passing through the frame being sent upwardly through the pipe, by means of air, to the water surface and discharged therefrom; or the external filtering type in which a filtration vessel is installed at the top of the tank and water is brought up by means of a pump, or the like, the treated water passing through the filtration vessel being allowed to drop down into the water tank. All of such systems, however, are extremely inferior in the purifying efficiency by means of aerobic bacteria because the activated sludge floats inside the tank during the circulation of the water, and in addition, since droppings from fish, leftover feed, and other dirt become deposited upon the filter layers and remain there undecomposed by means of bacteria, the same normally clog the filter layers within a month's time, and consequently, the same have to be removed at periodic intervals and cleaned for regeneration. Thus, substantial labor is required.
In such types of filtration tanks, the sludge formed from the dirt decomposed by means of aerobic bacteria clogs the filter medium making the passage of water therethrough quite difficult. In addition, the sludge itself becomes anaerobic thereby losing its purifying potential and adversely affects the filtration to a greater extent with an increasing amount of its deposition. Still further, the water inside the tanks cannot be uniformly circulated which results in an inhomogeneity in purification, whereby the water becomes anaerobic in a two month time period, and becomes stale, with the passage of a long period of time, which adversely affects the farm fish if the water is not replaced frequently. Moreover, these tanks are unable to render the inside active, with the oxygen in the atmosphere admixed insufficiently, and are not suitable for farming of salt-water fish in particular. In the case of a filtration system of the external filtration type which only deposits the treated water through a small opening into the water tank, the water near the position of deposition flows downwardly to be circulated, however, the farming water near the surface and located at a distance from the point of deposition remains still and is not substantially purified.